Degradation of dibenzothiophene and its metabolite 3-hydroxy-2-formylbenzothiophene by an environmental isolate

Microbial degradation of dibenzothiophene (DBT) beyond 3-hydroxy-2-formylbenzothiophene (HFBT), a commonly detected metabolite of the Kodama pathway for DBT metabolism, and the catabolic intermediates leading to its mineralization are not fully understood. The enrichment cultures cultivated from crude oil contaminated soil led to isolation of ERI-11; a natural mixed culture, selected for its ability to deplete DBT in basal salt medium (BSM). A bacterial strain isolated from ERI-11, and tentatively named A(11), degraded more than 90 % of the initial DBT (270 A mu M), present as the sole carbon and sulfur source, in 72 h. Gas chromatography-mass spectrophotometry (GC-MS) analyses of the DBT degrading A(11) culture medium extracts led to detection of HFBT. The metabolite HFBT, produced using A(11), was used in degradation assays to evaluate its metabolism by the bacteria isolated in this study. Ultra violet-visible spectrophotometry and high-performance liquid chromatography analyses established the ability of the strain A(11) to deplete HFBT, present as the sole sulfur and carbon source in BSM. GC-MS analyses showed the presence of 2-mercaptobenzoic acid in the HFBT degrading A(11) culture extracts. The findings in this study establish that the environmental isolate A(11) possesses the metabolic capacity to degrade DBT beyond the metabolite HFBT. The compound 2-mercaptobenzoic acid is an intermediate formed on HFBT degradation by A(11).